Carbon batteries played an important role in the history of fuel cell research. In 1855 Becquerel attempted to build a fuel cell that generated electricity by the electrochemical combustion of coal.1, 2 However, the electrolyte contained a nitrate that attacked the carbon without producing a current. By the end of the 19th century the increasing demand for electric power in Europe began to consume considerable amounts of coal because the conversion efficiency was very low.3 Contemplating this problem, in 1894 Ostwald3 called for development of a fuel cell that would react coal with oxygen to produce electricity more efficiently than thermo-mechanical equipment. Jacques3 demonstrated a 1.5 kW battery that employed a consumable carbon anode, an iron cathode, and an air-bubbled alkali hydroxide electrolyte to generate 0.9 V at 400-500° C. Operating intermittently, this battery delivered power with an overall efficiency of 32% during a six-month period. The experiment failed because carbonates accumulated in the electrolyte that halted the electrochemistry.3 In 1937 Baur and Preis2 tested a fuel cell that used a coke anode and an electrolyte composed of zirconia stabilized with magnesia or yttria at >1000° C. Summarizing the status of carbon fuel cell research as of 1969, Bockris and Srinivasen2 concluded that carbon fuel cells are impractical because (i) coal is not an electrical conductor, and (ii) graphite is too scarce and expensive to be used as a fuel.
Interest in carbon fuel cells resurfaced during the 1970's, when the Stanford Research Institute (SRI) attempted to develop a coal based fuel cell that employed molten lead at temperatures of 500 to 900° C.4, 5 Gur and Huggins6 demonstrated a high temperature (725 to 955° C.) fuel cell that employed stabilized zirconia as a solid electrolyte and a graphite anode.
Other consumable anodes in carbon fuel cells are disclosed by Pesavento7 and Tao8.
Charcoal is mentioned as an anode material, however raw charcoal is not a conductor of electricity. Charcoal is the carbonaceous residue of biomass pyrolysis (thermal decomposition in the absence of oxygen) or starved-air combustion (combustion with insufficient oxygen to permit complete combustion). A good quality charcoal has a fixed-carbon content as measured by ASTM D 1762-84 in excess of about 70%. Fixed-carbon contents above 70% may be realized by heating the charcoal to temperatures of about 400° to 500° C. A representative chemical formula for charcoal is CH0.60O0.13.8a When higher carbon content is desired, charcoal is carbonized by heat treatment in the absence of oxygen at temperatures above 500° C. Carbonized charcoals can have carbon contents in excess of 94 wt. %. Some carbonized charcoals are purer forms of carbon than natural graphites.
It is known that carbonized charcoal can possess very high electrical conductivities. In 1810 carbonized-charcoal electrodes were used in an arc lamp, and in 1830 carbonized charcoal was used as an electrode for primary batteries. These electrodes were made from powdered charcoal or coke bonded with sugar syrup or coal tar, pressed and carbonized at high temperatures.9 Others10-12 have reported extensive studies of biocarbon electrodes manufactured from charcoal particles bonded together by wood tar and subsequently carbonized. However, the high costs associated with molding, bonding, and carbonizing powdered charcoal makes this approach commercially impractical.
Accordingly, an object of the present invention is to provide an apparatus to enable carbonized-charcoal powder without bonding or molding to be used as an electrode in a fuel cell, battery or electrolyzer.
It is a further object of the present invention to provide carbonized-charcoal powder as the consumable anode of a biocarbon fuel cell.
It is a further object of the present invention to provide carbonized-charcoal powder as an electrode of a hydrogen fuel cell, battery or electrolyzer.
These and other objects and advantages to the present invention will be readily apparent upon reference to the drawing and the following description.